Answer:
The core of the U.S. Constitution has not been changed since its signing in 1776, which makes the U.S. Constitution the oldest in the world.
However, the Constitution has been amended. An amendment is an addition to the constitution that seeks to protect a particular right.
For example, after the civil war, the Thirteenth Amendment was approved. This amendment ended slavery and forced labor in the United States, except as a punishment for a crime, and sought to protect the rights of the recently liberated African Americans.
Another important amendment is the Thirteenth, which gave women the right to vote.
In conclusion, all the amendments in the United States have been additions to the U.S. Constitution with the goal of expanding the rights of people, and protecting those same rights.